On a wireless communications network, a multiple-input multiple-output (MIMO) wireless communications system may obtain a diversity gain and an array gain by using a precoding technology at a transmit end and a receive signal combination technology. A system using precoding may be expressed as:y=H{circumflex over (V)}s+N,where
Y is a receive signal vector, H is a channel matrix, {circumflex over (V)} is a precoding matrix, s is a transmit symbol vector, and N is measurement noise.
Generally, optimal precoding requires that channel state information (CSI) be fully known by a transmitter, and a commonly used method is that user equipment (UE) performs quantization on instantaneous CSI and reports the quantized instantaneous CSI to a base station. Generally, a receive end (for example, the UE) may obtain an estimated channel matrix H based on a reference signal, namely, the receive signal vector y, sent by a transmit end (for example, the base station), according to a known predefined transmitted pilot signal s, namely, the transmit symbol vector s, and the measurement noise N, or referred to as white Gaussian noise, and according to the formula: y=H{circumflex over (V)}s+n; and then select the precoding matrix {circumflex over (V)} that best matches the channel matrix H from a codebook, so that channel transmission quality and a channel transmission rate during actual data transmission are relatively high.
The user equipment includes a mobile station (MS), a relay, a mobile phone, a handset, portable equipment, or the like; the base station includes a NodeB base station (BS), an access point, a transmission point (TP), an evolved NodeB (eNB), a relay, or the like. CSI information reported by an existing Long Term Evolution (LTE) system includes information such as a rank indicator (RI), a precoding matrix indicator (PMI), and a channel quality indicator (CQI), where the RI and the PMI respectively indicate a quantity of used transport layers and a used precoding matrix. For a correspondence between a precoding matrix indicator PMI and a precoding matrix, reference can be made to the 3rd Generation Partnership Project (3GPP for short) TS 36.213, and each precoding matrix in which an element is included in a complex value is corresponding to one indicator number (a precoding matrix indicator PMI) in a codebook table. Generally, a set of used precoding matrices is referred to as a codebook, where each precoding matrix in the set is a code word in the codebook.
FIG. 1 is a schematic structural diagram of a one-dimensional linear array antenna. As shown in FIG. 1, distribution of the linear array antenna includes only one direction, and the direction is generally referred to as a horizontal direction. FIG. 2 is a schematic structural diagram of a two-dimensional planar array antenna. As shown in FIG. 2, distribution of the two-dimensional planar array antenna includes two directions: a horizontal direction and a vertical direction. An existing codebook is generally designed for a one-dimensional linear array. However, for two or more rows of antenna arrays, use of an existing precoding matrix in an array structure of a one-dimensional linear array antenna causes a decrease in precoding precision, thereby causing a relatively heavy loss in performance and a decrease in a system throughput.